Multi-scale detection of carbon fibres and voids in cementitious materials using Micro-CT with Gaussian filtering and ultrasonic total focusing method

The integration of carbon fibres (CFs) into cementitious materials has found wide applications in the construction field. The quality of fibre-reinforced cementitious composites (FRCCs) and their internal structure are essential for durability and safety. Non-destructive testing (NDT) like X-ray microtomography (micro-CT) is used to assess concrete defects and microstructures but faces challenges in accurately evaluating the spatial position of CFs in the cement-based matrix due to noise and segmentation limitations. Ultrasonic phased array testing shows promise for defect detection, yet its application for CFs in cementitious materials remains underexplored. In response to these challenges, this study developed and applied Gaussian filters to process micro-CT images, and in parallel, employed the ultrasonic total focusing method (TFM) as an efficient technique for detecting CF and voids in a cementitious matrix. Multi-scale features, including CFs and voids ranging from micrometres to millimetres, were examined. Micro-CT analysis provided high-resolution spatial visualisation and captured comprehensive details of the features within the specimens, while 1D ultrasonic phased array testing with the TFM method was able to detect the feature depth. The TFM method demonstrated high accuracy for deeper CF features, with errors of 3.26 % for CF bundles and 0 % for strips, when compared to micro-CT analysis. Void detection at mid-depth showed reliable performance, with errors of 3.40 % for small voids and 0.51 % for larger ones. This study advances the understanding and expands the practical application of NDT for FRCC characterisation, demonstrating enhanced feasibility for future industrial implementation.